1. Field
The present invention relates generally to transparent laminate structures for use in safety and security applications. Particularly, this invention relates to transparent laminate structures which require a forced entry protective threshold of various time intervals that comply with parallel standards as defined by the US Department of State. The invention within has been designed to provide successful test data outcomes for US Department of State forced entry standards through the use of the unique material combinations and lamination processes described. Specific combinations of rigid transparent substrates and energy absorbing substrates along with critical interlayer bonding materials yield a transparent laminate structure designed specifically to meet and/or exceed forced entry testing thresholds and standards outlined within this application.
2. Description of the Problem and Related Art
Significant prior art for this discovery includes U.S. patent pending application Ser. No. 12/690,588 from Ryan et al.
Impact resistant glass laminates were first introduced in the early 1900s and are well known in the art today for use in safety and security glass applications, and have been traditionally constructed using alternating layers of glass and plastic sheeting in the form of thermosets, or thermoplastics with adhesive and or heat bonding interlays. For example, bullet resistant glass is sometimes constructed with several glass sheets connected together with thin sheets of polyvinyl butyral, or polyester interposed there between with a polycarbonate or acrylic layer bonded on the inside face of the final glass sheet using a thermoplastic polyurethane layer. The polycarbonate or acrylic layer provides additional strength, and to a small degree, elasticity, to the glass upon impact but is used primarily to provide good resistance to spalling.
However, excessive layering of glass and polycarbonate or acrylic sheets creates problems. First, using such materials, the weight and thickness of the transparent laminar assembly requires a heavily engineered and reinforced support structure. Next, such laminar assemblies suffer delamination in the presence of heat, either localized heat from high-velocity projectile, heat from the bonding process, or ambient heat from, for example, desert environments. Additionally, current transparent laminar structures also suffer from other safety concerns such as leaching of biphenyl “A's”. Such characteristics decrease life cycle of the systems and structural stability, ultimately reducing or negating their effectiveness.
Other materials such as aromatics and ether-based have exhibited a great resistance to heat, and can provide desirable mechanical properties of greater elasticity and lighter weight. However, heretofore, such compositions have not been suitable for use in transparent armor because over time light transmissiveness degrades.
The US Department of State (DOS) has developed specific forced entry (FE) test standards and protocols to provide material suppliers base guidelines for product development to meet current and future needs. (US Department of State, SD-STD-01.01, Revision G (Amended)) Standards for forced entry (FE) protection include a 5 minute, 15 minute and a 60 minute standard. The FE tests involve a team of trained personnel in good health between 2 and 6 persons, which are given a pre-determined set of tools which number up to 31 tools in total who utilize those tools in an attempt to damage and penetrate the laminate panel which is being tested. The number of personnel and tools vary depending on which specific FE test standard is being tested for pass/failure. At the end of the timed and controlled test procedure, the test panel will be deemed either pass or fail. The certification of FE systems is mandatory and indicates that the systems will provide the level of FE protection required by DOS standards for specific facilities in certain threat environments. To date, the most difficult 60 minute test has been unattainable for transparent panels, but the invention herein provides a solution to meet and exceed that requirement.